1. Field of the Invention
The present invention relates to surveillance systems, and, more particularly, to security systems that receive signals from discrete sensors.
2. Description of the Related Art
Surveillance systems, also known as security systems, are known to include security devices, such as motion detectors, door sensors, window sensors, smoke detectors, etc., for monitoring a secured area of space. Most security systems have a range or variety of sensors to which the security system is connected. The manufacturers of the security systems develop sensors specifically for, and to be compatible with, their security systems. These sensors may be either hardwired to the system or may be in communication with the system via a wireless medium.
The security system may issue an alarm signal in response to one or more of the sensors detecting an event, such as a door or window opening, or the presence of a person within the secured area. The alarm signal may cause an audible alarm signal, such as a siren, to be issued. Alternatively, or in addition, the alarm signal may be electronically transmitted to a central monitoring station from which police may be summoned to investigate the breach of the security system. However, for a first type of sensor, sometimes referred to as a “perimeter sensor,” a grace period or “delay time” is provided between the tripping of the sensor and the issuance of the alarm signal. Such perimeter sensors are typically provided at exterior doors through which authorized users enter the premises. The delay time allows the authorized user to disarm the security system by entering a code at a control panel before the alarm signal is issued. For a second type of sensor, sometimes referred to as an “interior sensor,” no such delay time is provided between the tripping of the sensor and the issuance of the alarm signal. Such interior sensors are typically provided at locations at which an authorized user returning to the premises would not initially be sensed, such as within the interior of the building or at a window, for example.
When planning to leave the secured premises unoccupied, the user may arm the security system by entering a code into the control panel. The user is then typically provided with an arming exit delay time to leave the premises before the sensors are activated and the protection is thereby turned on. When a perimeter sensor is faulted (i.e., is found to not be operating correctly) at the end of the arming exit delay time, the faulted perimeter sensor is normally bypassed and a report of the malfunction is sent to central monitoring station and/or is displayed on the control panel. The control panel may also decide not to arm and declare an exit error, including sending a report of that exit error. In the first scenario, after the bypassing of the faulty perimeter sensor, the security system has no active perimeter sensor to initiate the entry delay timer. Thus, the possibility for false alarms is increased because interior sensors generate instant alarms before an authorized user has a chance to disarm the security system. That is, a delay time is not provided between the sensing of an event by the system and the issuance of an alarm signal.
What is needed in the art is a security system that can operate with a perimeter sensor faulted while avoiding false alarms in the form of instant alarms generated by interior sensors.